An electrochemical cell, in its simplest terms, consists of an anode (the oxidizing electrode), a cathode (the reducing electrode) and an electrolyte. In order for the electrochemical or electrolytic cell to function, the electrolyte must be compatible with the mechanisms of oxidation and reduction at the electrodes. As well, it must provide a conductive path for the transport of ionic species between the electrodes.
The electrochemical cell concept is broadly applied in industrial and scientific operations. Electrolytic cells are used in electroplating, water purification, and the production of high purity gases and metals while galvanic cells (batteries and fuel cells) provide a convenient means of energy storage and generation.
Also, due to their very high level of sensitivity, electrochemical cells are used for measurement in a variety of analytical procedures and many laboratory and process control instruments depend on the electrochemical cell as the sensing element for their function.
In the design of any electrochemical cell the choice of electrolyte is of importance. Considerable study has been given to identify the compositions and concentrations of electrolytes which will produce the best results in a wide variety of cell systems and applications.
In the utilization of electrochemical cells as sensing elements in analytical instruments, the requirement to maintain a consistent electrolyte composition is commonly required in order to ensure the accuracy of measurement. For example, in the determination of oxygen in fluids by electrochemical methods, this has been found to be the case. Further, in low temperature caustic electrolyte systems, the sample stream introduced into the electrolytic cell commonly contains components other than the one to be analyzed. These other components, for example, carbon dioxide, contained as a component in a stream for oxygen analysis result in a neutralization reaction forming neutralization products. This reduces the transfer of ions through the electrolyte causing drift of measurement in analysis. The problems of the neutralization products being formed in the electrolyte were overcome by the invention disclosed in U.S. Pat. No. 3,929,587. That invention allowed for oxygen level determinations in the presence of acid gases.
For some applications, it is desirable to be able to measure accurately and over long periods of time, levels of oxygen in the ppb range. Electrolytes inherently contain dissolved oxygen. This is not a problem when measuring in the ppm range. However, when measuring in the low ppb range, say between 1-10 ppb, the dissolved oxygen in the electrolyte contributes significantly to the measurement of oxygen from the gas sample.